Process for producing conjugated diene polymer, conjugated diene polymer, and rubber composition

ABSTRACT

A process for simply and inexpensively producing a conjugated diene polymer with a narrow molecular weight distribution and a high cis-bond content at a low cost is provided. The process comprises a polymerization step, wherein a conjugated diene polymer having a cis-1,4-bond content of 98.5 mass % or more and a ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography of 2.5 or less is obtained by carrying out a polymerization reaction in conjugated diene compounds using a catalyst composition containing a rare earth element-containing compound or a reaction product of the rare earth element-containing compound with a Lewis base, an aluminoxane and/or organoaluminum compound, and an iodine-containing compound.

TECHNICAL FIELD

The present invention relates to a conjugated diene polymer with anarrow molecular weight distribution and a high cis-bond content, aprocess for producing the same, and a rubber composition using theconjugated diene polymer.

BACKGROUND ART

A conjugated diene polymer plays a very important industrial role and isproduced by polymerizing a conjugated diene compound (monomer). A numberof polymerization catalysts used for the polymerization of a conjugateddiene compound have been proposed. Particularly, many polymerizationcatalysts have been studied and developed in order to produce aconjugated diene polymer with a high cis-1,4-bond content having highperformance in thermal and mechanical properties. For example, compositecatalysts having, as a major component, a transition metal compositioncontaining a transition metal such as nickel, cobalt, and titanium havebeen known, and some of these are widely used industrially as apolymerization catalyst for butadiene, isoprene, and the like (forexample, refer to Non-patent Document 1 and Patent Document 1).

In addition, as a polymerization catalyst exhibiting high polymerizationactivity which is capable of producing a conjugated diene polymer with ahigher cis-1,4-bond content, a composite catalyst comprising a rareearth metal-containing compound and an organometallic compound of ametal in the Group I to III has been researched and developed. Forexample, Patent Documents 2 to 4 disclose a method of producing aconjugated diene polymer by using a catalyst comprising a rare earthelement-containing compound, methyl almoxane (MAO), an organoaluminumcompound, and a halogen-containing compound. However, it has been stilldifficult to produce a polymer with a sufficiently narrow molecularweight distribution and a sufficiently high cis-1,4-bond content byusing the catalysts disclosed in these Patent Documents. Moreover, arubber composition produced from a conjugated diene polymer with acomparatively wide molecular weight distribution and a low cis-1,4-bondcontent cannot satisfy many characteristics such as mechanicalproperties, crack-growth resistance, and abrasion resistance, requiredfor a rubber used for tires.

-   [Patent Document 1] JP-B-37-8193-   [Patent Document 2] JP-A-10-306113-   [Patent Document 3] JP-A-11-35633-   [Patent Document 4] JP-A-2000-34320-   [Non-patent Document 1] Ind. Eng. Chem., 48,784 (1956)

DISCLOSURE OF THE INVENTION

The present invention has been completed in view of these problems inthe conventional technology and has an object of providing a process forproducing a conjugated diene polymer which can simply and inexpensivelyproduce a conjugated diene polymer with a narrow molecular weightdistribution and a high cis-bond content. Another object of the presentinvention is to provide a conjugated diene polymer with a narrowmolecular weight distribution and a high cis-bond content. Still anotherobject of the present invention is to provide a rubber compositionhaving high tensile strength, high tensile elongation, excellentcrack-growth resistance, and excellent abrasion resistance.

As a result of extensive studies in order to achieve the above objects,the inventors of the present invention have found that the above objectscan be achieved by polymerizing a conjugated diene compound using acatalyst composition comprising a rare earth element-containing compoundor a reaction product thereof with a Lewis base, an aluminoxane and/oran organoaluminum compound, and an iodine-containing compound. Thisfinding has led to the completion of the present invention.

Specifically, the following process for producing a conjugated dienepolymer, the conjugated diene polymer, and a rubber composition isprovided according to the present invention.

-   [1] A process for producing a conjugated diene polymer comprising a    polymerization step wherein a conjugated diene polymer having a    cis-1,4-bond content of 98.5 mass% or more and a ratio (Mw/Mn) of    the weight average molecular weight (Mw) to the number average    molecular weight (Mn) measured by gel permeation chromatography of    2.5 or less is obtained by carrying out a polymerization reaction in    conjugated diene compounds using a catalyst composition containing    the following components (a) to (c):

component (a): a rare earth element-containing compound which comprisesat least a rare earth element of an atomic number of 57 to 71 in theperiodic table, or a reaction product of the rare earthelement-containing compound with a Lewis base,

component (b): an aluminoxane and/or an organoaluminum compound shown bya general formula AlR1R2 R3, wherein R1 and R2 individually represent asame or different hydrocarbon group having 1 to 10 carbon atoms, or ahydrogen atom, and R3 represents a hydrocarbon group having 1 to 10carbon atoms which is same as or different from R1 and R2, and

component (c): an iodine-containing compound which comprises at leastone iodine atom in the molecular structure.

-   [2] The process for producing a conjugated diene polymer according    to [1], wherein the 1,2-vinyl content of the obtained conjugated    diene polymer is 0.3 mass % or less.-   [3] The process for producing a conjugated diene polymer according    to [1] or [2], wherein the polymerization reaction is carried out at    a temperature of 10° C. or higher.-   [4] The process for producing a conjugated diene polymer according    to any one of [1] to [3], wherein the molar ratio of the iodine atom    contained in the component (c) to the component (a), (iodine    atom)/(component (a)), is 0.5 to 3.-   [5] The process for producing a conjugated diene polymer according    to any one of [1] to [4], wherein the component (c) is (c1) a metal    iodide shown by a general formula R⁴ _(n)XI_(m) (wherein R⁴ is a    hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom, X    is a metal atom, n is an integer of 0 to 3, and m is an integer of 0    to 4), or (c2) a iodohydrocarbon compound shown by a general formula    R⁵I (wherein R⁵ is a hydrocarbon group having 1 to 20 carbon atoms).-   [6] A conjugated diene polymer produced by the process for producing    a conjugated diene polymer according to any one of [1] to [5].-   [7] A rubber composition comprising a rubber component (A) which    contains the conjugated diene polymer according to [6].-   [8] The rubber composition according to [7], comprising the rubber    component (A) and silica and/or carbon black (B).

[9] The rubber composition according to [8], wherein the rubbercomponent (A) contains the conjugated diene polymer in an amount of 20mass % or more, and the rubber composition contains silica and/or carbonblack (B) in an amount of 20 to 120 parts by mass per 100 parts by massof the rubber component (A).

According to the process for producing a conjugated diene polymer of thepresent invention, a conjugated diene polymer with a narrow molecularweight distribution and a high cis-bond content can be produced simplyand inexpensively. The conjugated diene polymer of the present inventionhas a narrow molecular weight distribution and a high cis-bond content.

Furthermore, the rubber composition of the present invention has hightensile strength, high tensile elongation, excellent crack-growthresistance, and excellent abrasion resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention are described below. Notethat the present invention is not limited to the following embodiments.Various modifications and improvements may be made to the embodimentswithout departing from the scope of the present invention based on theknowledge of a person skilled in the art.

1. Process for Producing Conjugated Diene Polymer

One embodiment of the process for producing a conjugated diene polymerof the present invention comprises a polymerization step wherein apolymerization reaction is carried out in conjugated diene compoundsusing a catalyst composition containing predetermined components (a) to(c). Details are described below.

(Catalyst Composition)

The catalyst composition used in the process for producing a conjugateddiene polymer according to the present embodiment contains the followingcomponents (a) to (c):

-   component (a): a rare earth element-containing compound which    comprises at least a rare earth element of an atomic number of 57 to    71 in the periodic table, or a reaction product of the rare earth    element-containing compound with a Lewis base,-   component (b): an aluminoxane and/or an organoaluminum compound    shown by the general formula AlR¹R²R³, wherein R¹ and R²    individually represent a same or different hydrocarbon group having    1 to 10 carbon atoms or a hydrogen atom, and R³ represents a    hydrocarbon group having 1 to 10 carbon atoms which is the same as    or different from R¹ and R², and-   component (c): an iodine-containing compound which comprises at    least one iodine atom in the molecular structure.

A conjugated diene polymer with a narrow molecular weight distributionand a high cis-1,4-bond content can be produced by polymerizingconjugated diene compounds (monomers) using this catalyst composition.More specifically, a conjugated diene polymer having a ratio of theweight average molecular weight (Mw) to the number average molecularweight (Mn) measured by gel permeation chromatography (GPC) (Mw/Mn) of2.5 or less, preferably 2.2 or less, and further preferably 2.0 or less,and a cis-1,4-bond content of 98.5 mass % or more, preferably 98.7 mass% or more, and further preferably 99.0 mass % or more can be produced.Moreover, this catalyst composition is not only less expensive than theconventionally-used metallocene catalyst, but also does not require apolymerization reaction at an extremely low temperature. For thisreason, the operation is simple and the catalyst composition is usefulin an industrial production process. Moreover, the amount of thecatalyst composition used may be smaller than the amount required whenthe metallocene catalyst is used. The smaller the amount of the catalystcomposition, the easier the deashing operation after the polymerizationreaction. Properties and characteristics of the resulting conjugateddiene polymer will be described later in detail.

(Component (a))

The component (a) contained in the catalyst composition used in theprocess for producing a conjugated diene polymer of the presentembodiment is a rare earth element-containing compound which comprisesat least a rare earth element of an atomic number of 57 to 71 in theperiodic table (that is, at least one lanthanoid series element), or areaction product obtained by the reaction of the rare earthelement-containing compound with a Lewis base. Neodymium, praseodymium,cerium, lanthanum, gadolinium, and the like can be given as specificexamples of the rare earth element. Neodymium is preferable among these.These rare earth elements can be used individually or in combination oftwo or more. As specific examples of the rare earth element-containingcompound, a carboxylate, an alkoxide, a β-diketone complex, a phosphate,a phosphite, and the like of the above-mentioned rare earth elements canbe given. Among these, a carboxylate or a phosphate is preferable, withthe carboxylate being more preferable.

As specific examples of the carboxylate of a rare earth element, a saltof carboxylic acid represented by a general formula (R⁶—CO₂)₃M (whereinM is a rare earth element of an atomic number from 57 to 71 of theperiodic table, and R⁶ is a hydrocarbon group having 1 to 20 carbonatoms) can be given. R⁶ in the general formula is preferably a saturatedor unsaturated alkyl group, and the alkyl group is preferably a linear,branched, or cyclic. The carboxyl group is bonded to a primary,secondary, or tertiary carbon atom. More specifically, salts of octanoicacid, 2-ethylhexanoic acid, oleic acid, stearic acid, benzoic acid,naphthenic acid, “Versatic acid” (a carboxylic acid having a carboxylgroup bonded to a tertiary carbon atom, manufactured by Shell ChemicalCo., Ltd.), and the like can be given. Among these, a salt of2-ethylhexanoic acid, a salt of naphthenic acid, and a salt of Versaticacid are preferable.

As specific examples of the alkoxide of a rare earth element, a compoundshown by a general formula (R⁷O)₃M (wherein M is a rare earth element ofan atomic number from 57 to 71 of the periodic table) can be given. Asspecific examples of the alkoxy group represented by R⁷⁰ in the generalformula, a 2-ethylhexylalkoxy group, an oleylalkoxy group, astearylalkoxy group, a phenoxy group, a benzylalkoxy group, and the likecan be mentioned. Among these, a 2-ethylhexylalkoxy group and abenzylalkoxy group are preferable.

As specific examples of the β-diketone complex of a rare earth element,an acetylacetone complex, a benzoylacetone complex, a propionitrileacetone complex, a valeryl acetone complex, an ethyl acetylacetonecomplex, and the like can be mentioned. Among these, an acetylacetonecomplex and an ethyl acetylacetone complex are preferable.

Specific examples of the phosphate or phosphite of a rare earth elementinclude rare earth element salts of bis(2-ethylhexyl)phosphate,bis(1-methylheptyl)phosphate, bis(p-nonylphenyl)phosphate,bis(polyethylene glycol-p-nonylphenyl)phosphate,(1-methylheptyl)(2-ethylhexyl)phosphate,(2-ethylhexyl)(p-nonylphenyl)phosphate,mono-2-ethylhexyl-2-ethylhexylphosphonate,mono-p-nonylphenyl-2-ethylhexylphosphonate,bis(2-ethylhexyl)phosphinate, bis(1-methylheptyl)phosphinate,bis(p-nonylphenyl)phosphinate,(1-methylheptyl)(2-ethylhexyl)phosphinate, and(2-ethylhexyl)(p-nonylphenyl)phosphinate. Among these, salts ofbis(2-ethylhexyl)phosphate, bis(1-methylheptyl)phosphate,mono-2-ethylhexyl-2-ethylhexyl phosphonate, and bis(2-ethylhexyl)phosphinate are preferable.

Among the rare earth element-containing compounds described above, aneodymium salt of phosphoric acid or a neodymium salt of carboxylic acidare preferred, with a neodyum salt of carboxylic acid such as neodymium2-ethylhexanoate, neodymium salt of Versatic acid being particularlypreferable.

In order to solubilize the above mentioned rare earth element-containingcompound in a solvent or to stably store for a long period of time, itis also preferable to use a mixture or a reaction product of the rareearth element-containing compound and a Lewis base. The amount of theLewis base is preferably 0 to 30 mol, and more preferably 1 to 10 mol,per 1 mol of the rare earth element. As specific examples of the Lewisbase, acetylacetone, tetrahydrofuran, pyridine, N,N-dimethylformamide,thiophene, diphenyl ether, triethylamine, an organic phosphorouscompound, a monohydric or dihydric alcohol, and the like can be given.The component (a) mentioned above can be used individually or incombination of two or more.

(Component (b))

The component (b) contained in the catalyst composition used in theprocess for producing the conjugated diene polymer of the presentembodiment is an aluminoxane and/or an organoaluminum compound shown bythe general formula AlR¹R²R³, wherein R¹ and R² individually represent asame or different hydrocarbon group having 1 to 10 carbon atoms, or ahydrogen atom, and R³ represents a hydrocarbon group having 1 to 10carbon atoms which is same as or different from R¹ and R².

Aluminoxane (almoxane) is a compound having a structure shown by thefollowing formula (1) or (2). The alumoxane may be an alumoxaneassociation product disclosed in Fine Chemicals, 23 (9), 5 (1994), J.Am. Chem. Soc., 115, 4971 (1993), and J. Am. Chem. Soc., 117, 6465(1995).

In the formulas (1) and (2), R⁸ is a hydrocarbon group having 1 to 20carbon atoms and n′ is an integer of 2 or more. As specific examples ofR⁸ in the formulas (1) and (2), methyl, ethyl, propyl, butyl, isobutyl,t-butyl, hexyl, iso-hexyl, octyl, and iso-octyl groups can be given.Among these, methyl, ethyl, isobutyl, and t-butyl groups are preferable,with the methyl group being more preferable. In the formulas (1) and(2), n′ is preferably an integer of 4 to 100.

As specific examples of aluminoxane, methylalmoxane (MAO),ethylalmoxane, n-propylalmoxane, n-butylalmoxane, isobutylalmoxane,t-butylalmoxane, hexylalmoxane, and iso-hexylalmoxane can be given.Aluminoxanes can be produced by a method known in the art, for example,a method of adding a trialkyl aluminum or a dialkyl aluminummonochloride to an organic solvent such as benzene, toluene, and xylene,further adding water, steam, steam-containing nitrogen gas, or a salthaving crystal water such as copper sulfate pentahydrate or aluminiumsulfate hexadecahydrate, and reacting the mixture. The abovealuminoxanes can be used individually or in combination of two or more.

As specific examples of the organoaluminum compound, trimethylaluminum,triethylaluminum, tri-n-propylaluminum, triisopropylaluminum,tri-n-butylaluminum, triisobutylaluminum, tri-t-butylaluminum,tripentylaluminum, trihexylaluminum, tricyclohexylaluminum,trioctylaluminum, hydrogenated diethylaluminum, hydrogenateddi-n-propylaluminum, hydrogenated di-n-butylaluminum, hydrogenateddiisobutylaluminum, hydrogenated dihexylaluminum, hydrogenateddiisohexylaluminum, hydrogenated dioctylaluminum, hydrogenateddiisooctylaluminum, ethylaluminum dihydride, n-propylaluminum dihydride,and isobutylaluminum dihydride can be given. Of these, preferableorganoaluminum compounds are triethylaluminum, triisobutylaluminum,hydrogenated diethylaluminum, and hydrogenated diisobutylaluminum. Theorganoaluminum compounds can be used individually or in combination oftwo or more.

(Component (C))

The component (c) contained in the catalyst composition used in theprocess for producing the conjugated diene polymer of the presentembodiment is an iodine-containing compound which contains at least oneiodine atom in its molecular structure. Any compounds containing atleast one iodine atom in its molecular structure such as trimethylsilyliodide, diethylaluminum iodide, zinc iodide, methyl iodide, butyliodide, hexyl iodide, octyl iodide, and iodine can be used as theiodine-containing compound without specific limitations. Preferableiodine-containing compounds are (c1) a metal iodide compound shown by ageneral formula R⁴ _(n)XI_(m) (wherein R⁴ is a hydrocarbon group having1 to 20 carbon atoms or a hydrogen atom, X is a metal atom, n is aninteger of 0 to 3, and m is an integer of 0 to 4) or (c2) aniodohydrocarbon compound shown by a general formula R⁵I (wherein R⁵ is ahydrocarbon group having 1 to 20 carbon atoms). As the metal atom of themetal iodide compound (c1), Si, Al, and Zn, for example, are preferable,with Si and Al being particularly preferable.

As specific examples of the metal iodide (c1), trimethylsilyl iodide,diethylaluminum iodide, zinc iodide, beryllium iodide, magnesium iodide,calcium iodide, barium iodide, cadmium iodide, mercury iodide, manganeseiodide, rhenium iodide, copper iodide, silver iodide, and gold iodidecan be given. Trimethylsilyl iodide and diethylaluminum iodide arepreferable among these. As specific examples of the iodohydrocarboncompound (c2), methyl iodide, butyl iodide, hexyl iodide, octyl iodide,iodoform, diiodomethane, and benzylidene iodide can be given. Butyliodide and hexyl iodide are preferable among these. Theseiodine-containing compounds may be used either individually or incombination of two or more.

(Catalyst Composition)

The amount of the components contained in the catalyst composition usedin the process for producing the conjugated diene polymer according tothe present embodiment can be appropriately determined as required. Thecomponent (a) is used in an amount preferably of 0.00001 to 1.0 mmol,and more preferably 0.0001 to 0.5 mmol per 100 g of the conjugated dienecompound. If the amount is below 0.00001 mmol, the polymerizationactivity tends to decrease. On the other hand, the amount of beyond 1.0mmol results in a high catalyst concentration which may require adeashing step.

When an aluminoxane is used as the component (b), the preferable amountof the aluminoxane contained in the catalyst composition can be shown bythe molar ratio of the component (a) to the aluminum (Al) contained inthe aluminoxane. That is, the molar ratio of the component (a) to thealuminum (Al) contained in the aluminoxane is preferably 1:1 to 1:500,more preferably 1:3 to 1:250, and particularly preferably 1:5 to 1:200.If the molar ratio is outside of the above range, the catalytic activitytends to decrease or a step of removing the catalyst residue may benecessary.

When an organoaluminum compound is used as the component (b), thepreferable amount of the organoaluminum compound contained in thecatalyst composition can be shown by the molar ratio of the component(a) to the organoaluminum compound. That is, the molar ratio of thecomponent (a) to the organoaluminum compound is preferably 1:1 to 1:700,and more preferably 1:3 to 1:500. If the molar ratio is outside of theabove range, the catalytic activity tends to decrease or a step ofremoving the catalyst residue may be necessary.

Moreover, a preferable amount of the component (c) contained in thecatalyst composition can be shown by the molar ratio of the iodine atomin the component (c) to the component (a). That is, the ratio of (iodineatom)/(component (a)) (molar ratio) is preferably 0:5 to 3, morepreferably 1 to 2.5, and particularly preferably 1.2 to 1.8. If themolar ratio of (iodine atom)/(component (a)) is below 0.5, thepolymerization catalyst activity tends to decrease. On the other hand,if the molar ratio of (iodine atom)/(component (a)) is beyond 3, theiodine tends to act as a catalyst poison.

In addition to the components (a) to (c), the catalyst composition mayoptionally contain a conjugated diene compound and/or a non-conjugateddiene compound in an amount of preferably not more than 1000 mol, morepreferably 150 to 1000 mol, and particularly preferably 3 to 300 mol.Since the catalyst activity is further increased, the catalystcomposition preferably contains the conjugated diene compound and/or thenon-conjugated diene compound. Examples of the conjugated diene compoundused here are same as the monomers for the polymerization such as1,3-butadiene and isoprene which are described later. As examples of thenon-conjugated diene compound, divinylbenzene, diisopropenyl benzene,triisopropenylbenzene, 1,4-vinylhexadiene, and ethylidenenorbornene canbe given.

(Preparation of Catalyst Composition)

The catalyst composition used in the process for producing theconjugated diene polymer according to the present embodiment can beprepared by, for example, reacting the components (a) to (c) dissolvedin a solvent with optionally-added conjugated diene compounds and/ornon-conjugated diene compounds. The order of addition of each componentis arbitrary, provided that it is preferable to previously mix and reactthe components and age the reaction product in order to increase thecatalyst activity and to reduce the polymerization initiation inductionperiod. The aging temperature is preferably 0 to 100° C., and morepreferably 20 to 80° C. If the temperature is below 0° C., the agingtends to be insufficient. If the temperature is beyond 100° C., on theother hand, the catalytic activity tends to decrease and the molecularweight distribution tends to broaden. There are no particularlimitations to the aging time. Before adding to a polymerizationreaction vessel, the components may be caused to come in contact witheach other in the lines. An aging time of 0.5 minutes or longer issufficient. The prepared catalyst composition is stable for severaldays.

(Conjugated Diene Compound (Monomer))

The monomers used for polymerization in the process for producing theconjugated diene polymer of the present embodiment are conjugated dienecompounds. As specific examples of this conjugated diene compound,1,3-butadiene, 2-methyl-1,3-butadiene (isoprene),2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, myrcene, andcyclo-1,3-pentadiene can be given. Among these, 1,3-butadiene, isoprene,and 1,3-pentadiene are preferable. These conjugated diene compounds maybe used individually or in combination of two or more. A copolymer isobtained when two or more conjugated diene compounds are used.

(Polymerization step)

The polymerization step in the process for producing the conjugateddiene polymer in the present embodiment comprises carrying out apolymerization reaction in conjugated diene compounds using a catalystcomposition containing the components (a) to (c). The polymerizationreaction may be carried out either in the presence or absence of apolymerization solvent. An inert organic solvent is preferably used asthe polymerization solvent. As specific examples of the organic solventsuitably used, saturated aliphatic hydrocarbons having 4 to 10 carbonatoms such as butane, pentane, hexane, and heptane; saturated alicyclichydrocarbons having 4 to 20 carbon atoms such as cyclobutane,cyclopentane, and cyclohexane; monoolefins such as 1-butene and2-butene; aromatic hydrocarbons such as benzene, toluene, and xylene;and halogenated hydrocarbons such as methylene chloride, chloroform,carbon tetrachloride, trichloroethylene, perchloroethylene,1,2-dichloroethane, chlorobenzene, bromobenzene, and chlorotoluene canbe given. These polymerization solvents may be used either individuallyor in combination of two or more.

The polymerization reaction is carried out preferably at a temperatureof 10° C. or more, more preferably 10 to 50° C., and particularlypreferably 10 to 30° C. If the temperature is below 10° C., thecatalytic activity tends to decrease and the molecular weightdistribution of the resulting polymer tends to broaden. Thepolymerization reaction may be carried out either by a batch operationor a continuous operation. It is preferable to prevent thepolymerization system from being contaminated by deactivating substancesor compounds such as oxygen, water, carbon dioxide, or the like in orderto prevent deactivation of the catalyst composition and the polymer. Thepolymerization reaction may be carried out in the presence of hydrogengas in order to adjust the molecular weight of the resulting conjugateddiene polymer.

2. Conjugated Diene Polymer

The conjugated diene polymer of the present invention is produced by theabove-mentioned production process and has a cis-1,4-bond content of98.5 mass % or more and a ratio (Mw/Mn) of the weight average molecularweight (Mw) and the number average molecular weight (Mn) measured by gelpermeation chromatography (GPC) of 2.5 or less. Details are describedbelow.

(Cis-1,4-Bond Content)

The conjugated diene polymer of the present embodiment has acis-1,4-bond content of 98.5 mass % or more, preferably 98.7 mass % ormore, and more preferably 99.0 mass % or more. If the cis-1,4-bondcontent is below 98.5 mass %, mechanical properties such as tensilestrength and tensile elongation, crack-growth resistance, and abrasionresistance of a vulcanized rubber obtained from the conjugated dienepolymer may not be sufficient. Although the upper limit of thecis-1,4-bond content is not particularly limited, such an upper limit is99.5 mass % from the viewpoint of practical productivity. Thecis-1,4-bond content of the conjugated diene polymer in the embodimentcan be easily adjusted by controlling the polymerization temperature.

(Mw/Mn)

The ratio (Mw/Mn) of the weight average molecular weight (Mw) to thenumber average molecular weight (Mn) of the conjugated diene polymer ofthe present embodiment measured by GPC is 2.5 or less, preferably 2.2 orless, and more preferably 2.0 or less. If the Mw/Mn ratio is beyond 2.5,mechanical properties such as tensile strength and tensile elongation,crack-growth resistance, and abrasion resistance of a vulcanized rubberobtained from the conjugated diene polymer may not be sufficient.Although the lower limit of the Mw/Mn ratio is not particularly limited,the Mw/Mn ratio is 0.5 or more from the viewpoint of practicalproductivity. The Mw/Mn ratio of the conjugated diene polymer in thepresent embodiment can be easily adjusted by controlling the molar ratioof the components (a) to (c) contained in the catalyst composition.

The 1,2-vinyl bond content of the conjugated diene polymer of thepresent embodiment is preferably 0.3 mass % or less, more preferably 0.1to 0.3 mass %, and particularly preferably 0.1 to 0.15 mass %. If the1,2-vinyl bond content is beyond 0.3 mass %, mechanical properties suchas tensile strength, tensile elongation, crack-growth resistance, andabrasion resistance of a vulcanized rubber obtained from the conjugateddiene polymer may not be sufficient.

Mooney viscosity (ML₁₊₄ (100° C.)) of the conjugated diene polymer ofthe present embodiment is preferably 10 to 100, and more preferably 20to 50. If the Mooney viscosity (ML₁₊₄ (100° C.)) is below 10, mechanicalproperties such as tensile strength, tensile elongation, crack-growthresistance, and abrasion resistance of a vulcanized rubber obtained fromthe conjugated diene polymer may not be sufficient. If the Mooneyviscosity (ML₁₊₄ (100° C.)) is beyond 100, processability during akneading operation decreases and the mechanical properties of theresulting vulcanized rubber tends to be poor.

3. Rubber Composition

One embodiment of the rubber composition of the present inventioncomprises the rubber component (A) which contains the above-mentionedconjugated diene polymer. Details are described below.

((A) Rubber Component)

The rubber component (A) contained in the rubber composition of thepresent embodiment contains the above-mentioned conjugated dienepolymer. The content of the conjugated diene polymer in the rubbercomponent (A) is preferably 20 mass % or more, more preferably 30 mass %or more, and particularly preferably 40 mass % or more. If the contentof the conjugated diene polymer in the rubber component (A) is below 20mass %, mechanical properties such as tensile strength, tensileelongation, crack-growth resistance, and abrasion resistance of avulcanized rubber obtained from the conjugated diene polymer tend tobecome insufficient.

The rubber component (A) may contain only one type of the conjugateddiene polymer or may contain two or more types of the conjugated dienepolymer. The rubber component (A) may contain rubber components otherthan the conjugated diene polymer. As examples of such other rubbercomponents, natural rubber, synthetic isoprene rubber, butadiene rubber,styrene-butadiene rubber, ethylene-α-olefin copolymer rubber,ethylene-α-olefin-diene copolymer rubber, acrylonitrile-butadienecopolymer rubber, chloroprene rubber, and halogenated butylene rubber,and mixtures of these rubbers can be given. A part of such other rubbercomponents may be polyfunctionalized to have, for example, a branchedstructure by treatment with a modifier such as tin tetrachloride orsilicon tetrachloride.

((B) Silica, Carbon Black)

The rubber composition of the present embodiment preferably contains (B)silica and/or carbon black. As specific examples of silica, wet silica(hydrous silicic acid), dry silica (silicic acid anhydride), calciumsilicate, and aluminum silicate can be given. Among these, wet silica ispreferable due to the effect of improving fracture resistance and themost remarkable effect of maintaining both excellent wet gripcharacteristic and excellent low rolling resistance. These silicas maybe used either individually or in combination of two or more.

SRF, GPF, FEF, HAF, ISAF, and SAF can be given as specific examples ofthe carbon black. Carbon black having iodine adsorption (IA) of 60 mg/gor more and dibutyl phthalate oil absorption (DBP) of 80 ml/100 g ormore is preferable. The effect of improving grip performance andfracture resistance is increased by using the carbon black. HAF, ISAF,and SAF excelling in wear resistance are particularly preferred. Thesecarbon blacks may be used either individually or in combination of twoor more.

In the rubber composition of the present embodiment, silica and/orcarbon black (B) are used in an amount of preferably 20 to 120 parts bymass per 100 parts by mass of the rubber component (A), and morepreferably 25 to 100 parts by mass from the viewpoint of reinforcementand the improvement effect of many other properties associated with thereinforcement. If the amount of the silica and/or carbon black (B) issmall, the improvement effect of fracture resistance and the like tendsto be insufficient. If the amount of the silica and/or carbon black (B)is large, on the other hand, the processability of the rubbercomposition tends to decrease.

When silica is added to the rubber composition of the present embodimentas a filler for reinforcement, it is preferable to blend a silanecoupling agent in order to further increase the reinforcing effect. Asexamples of the silane coupling agent,bis(3-triethoxysilylpropyl)tetrasulfide,bis(3-triethoxysilylpropyl)trisulfide,bis(3-triethoxysilylpropyl)disulfide,bis(2-triethoxysilylethyl)tetrasulfide,bis(3-trimethoxysilylpropyl)tetrasulfide,bis(2-trimethoxysilylethyl)tetrasulfide,3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane,3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-trimethoxysilylpropylbenzothiazolyl tetrasulfide,3-triethoxysilylpropylbenzolyl tetrasulfide,3-triethoxysilylpropylmethacrylate monosulfide,3-trimethoxysilylpropylmethacrylate monosulfide,bis(3-diethoxymethylsilylpropyl)tetrasulfide,3-mercaptopropyldimethoxymethylsilane,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, anddimethoxymethylsilylpropylebenzothiazolyl tetrasulfide can be given.Among these, bis(3-triethoxysilylpropyl)polysulfide and3-trimethoxysilylpropylbenzothiazil tetrasulfide are suitable from theviewpoint of the improvement effect of reinforcing properties and thelike. These silane coupling agents can be used individually or incombination of two or more.

Although the amount of the silane coupling agent added differs accordingto the type of the silane coupling agent used, an amount of 1 to 20 mass% per 100 mass % of the silica is preferable, with a more preferableamount being 3 to 15 mass %. If the amount is below 1 mass %, it issometimes difficult for the coupling agent to exhibit its effect. If theamount is beyond 20 mass %, on the other hand, the rubber componenttends to become gelled.

Various chemicals, additives, and the like which are commonly used inthe rubber industry can be optionally added to the rubber composition ofthe present embodiment to the extent that the objective of the presentinvention is not impaired. A vulcanizing agent, a vulcanizationaccelerator, process oil, an aging preventive, an antiscorching agent,zinc oxide, stearic acid, and the like can be given as chemicals,additives, and the like which can be added to the rubber composition ofthe present embodiment.

The rubber composition of the present invention can be produced bykneading using an open-type kneader such as a roller or a closed-typekneader such as a Banbury mixer. The rubber composition is applicable tovarious rubber goods by vulcanizing after molding. The rubbercomposition of the present embodiment is suitable for use in tireapplications such as tire treads, under treads, carcasses, sidewalls,and beads, and other industrial articles such as a rubber vibrationinsulator, a fender material, a belt, a hose, and the like. The rubbercomposition of the present embodiment is particularly suitably used as atire tread rubber.

EXAMPLES

The present invention is described below in detail by way of examples.Note that the present invention is not limited to the followingexamples. In the examples, “part(s)” means “part(s) by weight” and “%”means “wt %” unless otherwise indicated. The following are methods formeasuring values for various properties and evaluating characteristics.

-   Mooney viscosity (ML₁₊₄, 100° C.): measured under the conditions of    a preheating time of 1 minute and a measuring time of 4 minutes at a    temperature of 100° C.-   Molecular weight distribution (Mw/Mn): measured using a gel    permeation chromatograph (“HLC-8120GPC” manufactured by Tosoh Corp.)    and a differential refractometer as a detector under the following    conditions.-   Column: “GMHHXL” manufactured by Tosoh Corp.-   Mobile phase: tetrahydrofuran-   Cis-1,4 bond content (%), 1,2-vinyl bond content (%): ¹H-NMR    analysis was conducted to measure signal intensities at 5.30 to 5.50    ppm (1,4-bond) and at 4.80 to 5.01 ppm (1,2-bond). The ratio of    1,4-bond to 1,2-bond in the polymer was calculated from the results.    In addition, ¹³C-NMR analysis was conducted to measure signal    intensities at 27.5 ppm (cis-1,4-bond) and at 32.8 ppm    (trans-1,4-bond). The ratio of cis-1,4-bond to trans-1,4-bond in the    polymer was calculated from the results. Cis-1,4 bond content (%)    and 1,2-vinyl bond content (%) were calculated from these ratios.-   Tensile strength (T_(B) (MPa)), 300% modulus (M₃₀₀ (MPa)): Tensile    strength (T_(B) (MPa)) and 300% modulus (M₃₀₀ (MPa)) were measured    according to JIS K6301.-   Crack-growth resistance: A 0.5 mm crack was formed at the center of    a No. 3 test specimen specified in JIS K6251-1993. A 100% stress was    repeatedly applied at room temperature to determine the number of    times of stress application at which the test specimen was parted.    The results were converted into indices taking the determined number    of times obtained for the vulcanized rubber of Comparative Example 3    as 100. The larger the index, the better the crack-growth    resistance.-   Wear resistance: An amount of wear (g) was measured using a    Lambourn-type abrader (manufactured by Shimada Giken Co., Ltd.) at a    slip ratio of 60% at room temperature according to JIS K6246. The    results were converted into indices taking the determined amount of    wear obtained for the vulcanized rubber of Comparative Example 3    as 100. The larger the index, the better the wear resistance.

Example 1

A 5 L autoclave of which the internal atmosphere was replaced bynitrogen was charged with 2.4 kg of cyclohexane and 300 g of1,3-butadiene. The autoclave was further charged with a catalystcomposition (iodine atom/rare earth element-containing compound (molarratio)=2.0) obtained by reacting a cyclohexane solution of neodymiumversatate (Nd(ver)₃) (0.18 mmol), a toluene solution of methyl alumoxane(MAO) (1.8 mmol), hydrogenated diisobutylaluminum (AlBu₂H) (5.3 mmol),and a toluene solution of trimethylsilyl iodide (Me₃SiI) (0.36 mmol)with 1,3-butadiene in an amount of 5 times the mols of neodymium andaging at 50° C. for 30 minutes, to carry out a polymerization reaction1,3-butadiene at 30° C. for 2 hours. Then, a methanol solutioncontaining 2,4-di-tert-butyl-p-cresol (1.5 g) was added to terminate thepolymerization reaction. The solvent was removed by steam stripping andthe residue was dried by a roller at 110° C. to obtain 295 g of polymer.The Mooney viscosity (ML₁₊₄, 100° C.) of the resulting polymer was 32,the molecular weight distribution (Mw/Mn) was 1.7, the cis-1,4-bondcontent was 99.5 mass %, and the 1,2-vinyl bond content was 0.17 mass %.

100 parts of the obtained polymer, 50 parts of HAF carbon black, 3 partsof zinc oxide, 2 parts of stearic acid, 1 part of an aging preventive(N-isopropyl-N′-phenyl-p-phenylenediamine), 0.8 parts of vulcanizationaccelerator (N-cyclohexyl-2-benzothiazilsulfeneamide), and 1.5 parts ofsulfur were kneaded in a plastmill. The kneaded mixture waspress-vulcanized at 145° C. to obtain a vulcanized rubber. The resultingvulcanized rubber had tensile strength (T_(B)) of 21.2 MPa, 300% modulus(M₃₀₀) of 9.6 MPa, crack-growth resistance (index) of 181, and wearresistance (index) of 138.

Examples 2 to 8 and Comparative Examples 1 and 2

Polymers were obtained in the same manner as in Example 1 except forusing components for the catalyst compositions and the polymerizationconditions (temperature and time) shown in Table 1. Yields of thepolymers obtained are shown in Table 1. Values for various properties ofthe obtained polymers are shown in Table 3. Vulcanized rubbers wereobtained using the polymers according to the compositions shown in Table2 by kneading and press vulcanization. Values for various properties ofthe vulcanized rubbers are shown in Table 3.

Comparative Example 3

Polybutadiene rubber (“BR01” manufactured by JSR Corp.) was used as apolymer of Comparative Example 3. Values for various properties of thepolymer are shown in Table 3. Vulcanized rubber was obtained using thepolymer according to the composition shown in Table 2 by kneading andpress vulcanization. Values for various properties of the vulcanizedrubbers are shown in Table 3.

TABLE 1 Iodine atom/ Rare earth rare earth Polymer- element-containingOrganoaluminum Iodine-containing element- ization Polymer- compoundAluminoxane compound compound containing temper- ization Yield of AmountAmount Amount Amount compound ature time polymer Type (mmol) Type (mmol)Type (mmol) Type (mmol) (molar ratio) (° C.) (h) (g) Example 1 Nd (ver)₃0.18 MAO 1.8 AlBu₂H 5.3 Me₃SiI 0.36 2.0 30 2 295 2 Nd (ver)₃ 0.18 MAO1.8 AlBu₂H 4.8 Me₃SiI 0.36 2.0 50 2 295 3 Nd (ver)₃ 0.18 MAO 1.8 AlBu₂H7.3 Me₃SiI 0.36 2.0 −10 2 50 4 Nd (ver)₃ 0.18 MAO 1.8 AlBu₂H 6.5 Me₃SiI0.08 0.4 30 2 170 5 Nd (ver)₃ 0.18 MAO 1.8 AlBu₂H 6.5 Me₃SiI 0.6 3.3 302 190 6 Nd (ver)₃ 0.18 MAO 1.8 AlBu₂H 5.3 BuI 0.36 2.0 30 2 290 7 Nd(ver)₃ 0.18 MAO 1.8 AlBu₂H 5.3 Et₂AlI 0.36 2.0 30 2 280 8 Nd (ver)₃ 0.18MAO 1.8 AlBu₂H 5.3 ZnI₂ 0.18 2.0 30 2 285 Comparative 1 Nd (ver)₃ 0.18MAO 1.8 Al(i-Bu)₂H 5.3 Me₃SiCl 0.36 — 30 2 295 Example 2 Nd (ver)₃ 0.18MAO 9 Al(i-Bu)₂H 3.7 Me₃SiCl 0.36 — 30 2 295 3 — — — — — — — — — — — —

TABLE 2 Composition Part Polymer 100 HAF carbon black 50 Zinc oxide 3Stearic acid 2 Aging preventive*¹ 1 Vulcanization accelerator*² 0.8Sulfur 1.5 *¹N-isopropyl-N′-phenyl-p-phenylenediamine*²N-cyclohexyl-2-benzothiazil sulfeneamide

TABLE 3 Properties of polymer Molecular Properties of vulcanized rubberweight Cis-1,4-bond 1,2-vinyl bond Crack-growth Wear Mooney viscositydistribution content content T_(B) M₃₀₀ resistance resistance(ML₁₊₄(100° C.)) (Mw/Mn) (%) (%) (MPa) (MPa) (index) (index) Example 132 1.7 99.5 0.17 21.2 9.6 181 138 2 37 1.5 99.1 0.25 20.4 9.1 174 131 329 1.9 99.7 0.11 21.5 9.9 195 146 4 34 1.9 99.2 0.22 20.3 9.0 172 129 533 1.8 98.8 0.24 20.4 9.1 173 130 6 31 1.8 99.4 0.18 21.1 9.6 180 136 729 2.0 98.8 0.33 19.7 8.7 164 124 8 33 2.0 98.7 0.34 19.8 8.8 164 123Comparative 1 30 3.7 98.2 0.35 19.3 8.3 153 109 Example 2 36 2.8 96.80.87 18.9 8.1 143 112 3 45 4.8 94.5 2.52 16.3 7.5 100 100

As shown in Table 3, it is clear that the conjugated diene polymers ofExamples 1 to 8 have a narrow molecular weight distribution, a highcis-1,4-bond content, and a low 1,2-vinyl bond content as compared withthe conjugated diene copolymers of Comparative Examples 1 to 3. It isalso clear that the vulcanized rubber made from the conjugated dienecopolymers of Examples 1 to 8 have excellent mechanical properties suchas tensile strength and modulus, crack-growth resistance, and wearresistance.

In particular, it was confirmed that due to inclusion of the metaliodide compound shown by the general formula R⁴ _(n)XI_(m) (c1) or theiodohydrocarbon compound (c2) shown by the general formula R⁵I as thecomponent (c), the conjugated diene copolymers of Examples 1 to 6 showeda 1,2-vinyl bond content of 0.3 mass % or less and excellent mechanicalproperties such as tensile strength and modulus, excellent crack-growthresistance, and excellent wear resistance.

Examples 9 to 11 and Comparative Examples 4 and 5

Vulcanized rubbers were obtained each using the polymer of Example 1, 2,or 6, or Comparative Example 1 or 3 according to the compositions shownin Table 4 by kneading and press vulcanization. Values of variousproperties of the vulcanized rubbers are shown in Table 5.

TABLE 4 Composition Part Polymer 40 Natural rubber 60 HAF carbon black50 Zinc oxide 3 Stearic acid 2 Aging preventive*¹ 1 Vulcanizationaccelerator*² 0.8 Sulfur 1.5 *¹N-isopropyl-N′-phenyl-p-phenylenediamine*²N-cyclohexyl-2-benzothiazil sulfeneamide

TABLE 5 Properties of vulcanized rubber Crack- growth Wear T_(B) M₃₀₀resistance resistance Polymer (MPa) (Mpa) (index) (index) Example 9Example 1 24.9 13.7 151 128 Example 10 Example 2 25.4 13.3 141 122Example 11 Example 6 24.9 13.6 152 126 Comparative Comparative 23.9 12.8121 114 Example 4 Example 1 Comparative Comparative 23.4 12.2 100 100Example 5 Example 3

As shown in Table 5, it is clear that the vulcanized rubbers made fromthe compositions containing the conjugated diene copolymers of Examples9 to 11, each blended with a natural rubber, have excellent mechanicalproperties such as tensile strength and modulus, crack-growthresistance, and wear resistance as compared with the vulcanized rubbersmade from the compositions containing the conjugated diene copolymers ofComparative Example 4 or 5.

INDUSTRIAL APPLICABILITY

The rubber composition containing the conjugated diene polymer of thepresent invention can be suitably used for tire applications such astire treads, under treads, carcasses, side walls, and beads, as well asother industrial products such as vibration-proof rubber, fender beams,belts, and hoses. The rubber composition is particularly preferable as atire tread rubber.

The invention claimed is:
 1. A process for producing a conjugated dienepolymer comprising a polymerization wherein a conjugated diene polymerhaving a cis-1,4-bond content of 98.5 mass % or more and a ratio (Mw/Mn)of the weight average molecular weight (Mw) to the number averagemolecular weight (Mn) measured by gel permeation chromatography of 2.5or less is obtained by carrying out a polymerization reaction inconjugated diene compounds using a catalyst composition comprising thefollowing components (a) to (c): component (a): a rare earth elementcomprising compound which comprises at least a rare earth element of anatomic number of 57 to 71 in the periodic table, or a reaction productof the rare earth element comprising compound with a Lewis base,component (b): an aluminoxane and organoaluminum compound shown by ageneral formula AlR¹ R² R³, wherein R¹ and R² individually represent asame or different hydrocarbon group having 1 to 10 carbon atoms or ahydrogen atom, and R³ represents a hydrocarbon group having 1 to 10carbon atoms which is the same as or different from R¹ and R², andcomponent (c): iodine.
 2. The process for producing a conjugated dienepolymer according to claim 1, wherein the 1,2-vinyl content of theobtained conjugated diene polymer is 0.3 mass % or less.
 3. The processfor producing a conjugated diene polymer according to claim 1, whereinthe polymerization reaction is carried out at a temperature of 10° C. orhigher.
 4. The process for producing a conjugated diene polymeraccording to claim 1, wherein the molar ratio of the iodine atomcontained in the component (c) to the component (a), (iodineatom)/(component (a)), is 0.5 to
 3. 5. A conjugated diene polymerproduced by the process for producing a conjugated diene polymeraccording to claim
 1. 6. A rubber composition comprising a rubbercomponent (A) which contains the conjugated diene polymer according toclaim
 5. 7. The rubber composition according to claim 6, comprising therubber component (A) and silica and/or carbon black (B).
 8. The rubbercomposition according to claim 7, wherein the rubber component (A)contains the conjugated diene polymer in an amount of 20 mass % or more,and the rubber composition contains silica and/or carbon black of thecomponent (B) in an amount of 20 to 120 parts by mass per 100 parts bymass of the rubber component (A).
 9. The process of claim 1, wherein inthe process, the rare earth element-comprising compound comprisesneodymium.
 10. The process of claim 1, wherein in the process, the rareearth element-comprising compound comprises praseodymium.
 11. Theprocess of claim 1, wherein in the process, the rare earthelement-comprising compound comprises cerium.
 12. The process of claim1, wherein in the process, the rare earth element-comprising compoundcomprises lanthanum.
 13. The process of claim 1, wherein in the process,the rare earth element-comprising compound comprises gadolinium.
 14. Theprocess of claim 1, wherein in the process, the rare earthelement-comprising compound is a phosphate.
 15. The process of claim 1,wherein in the process, the rare earth element-comprising compound is acarboxylate.
 16. The process of claim 1, wherein in the process, thecomponent (a) comprises the product obtained by the reaction of the rareearth element-comprising compound with a Lewis base.
 17. The process ofclaim 1, wherein in the process, in the component (b), R¹ is a hydrogenatom.
 18. The process of claim 1, wherein in the process, in thecomponent (b), R² is a hydrogen atom.